Compressors, expandors, signal amplifiers and amplitude and angle modulators of the prior art depend generally on approximation methods in which the amplitude of a signal modulates a d-c voltage or a carrier by means of non-linear circuit elements, with any resulting error in the modulated wave being reduced by negative feedback or other means. We do not know of any prior patent art, publications or apparatus which use invariable quantizing elements to produce modulated d-c or a-c waves which accurately represent the signals, or to produce compressed or expanded signals which follow a precise law.